Postretirement Benefits - Pension Amounts Recorded Within Account Line Items of Balance Sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Sep. 30, 2016
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Accrued compensation and benefits	$ 112	$ 155
Long-term pension liability	1,424	1,958
Pension and Other Postretirement Defined Benefit Plans, Liabilities	$ 1,536	$ 2,113